The defocusing amount is an important parameter that affects the cutting quality in the laser cutting process. In the oxygen free cutting of stainless steel plates, the auxiliary gas is used to blow off the molten residue to reduce the amount of residue. The cutting quality is very important. Therefore, the focus position needs to be set inside the steel plate to expand the notch width to increase the flow of auxiliary gas

The selection of defocusing amount has a great impact on the cutting quality of stainless steel plate:

【1】 When the focus position is appropriate, the slit material melts, while the material near the cutting edge does not melt, and the slag is blown away, forming a clean slit without slag.

【2】 When the focus position is backward, the energy absorbed by the unit area of the lower part of the cutting material is reduced, and the cutting energy is weakened, resulting in that the material cannot be completely melted and blown away by the auxiliary gas, so that the incompletely melted material is attached to the lower surface of the cutting plate.

【3】 When the focus position is advanced, the average energy absorbed per unit area in the lower half of the cutting material increases, leading to the melting of the material cut and the material near the cutting edge, and the liquid flow. At this time, because the auxiliary air pressure and cutting speed are unchanged, the melted material adheres to the lower surface of the material in a spherical form, and forms slag.

In actual production, the focus of laser cutting stainless steel plate is required to be selected on or below the material surface. This is because the width of the upper part of the cutting groove is enlarged, the fluidity of gas and melt is improved, the smooth range of the section is expanded, and the cutting quality is improved.

During the cutting process, for steel plates of different thicknesses, the focus position is also not fixed. When the focus position is taken on or above the surface of the steel plate, due to the low average power density of the lower part of the steel plate and insufficient energy, it is easy to produce slag on the lower surface. Therefore, when laser cutting stainless steel plate, the focus position should be selected inside the material. To improve the fluidity of gas and molten metal, ensure that the lower part has sufficient energy density, so that the range of the smooth surface is expanded.